Microstructure and Mechanical Properties of Sn-Ag-Cu Nanocomposite Solders: A Review

Abstract

Sn-Ag-Cu (SAC) solder alloy is the most promising lead-free solder alloy, with Sn as the principal constituent. It offers excellent solderability and mechanical properties and addresses the environmental hazards associated with Pb-Sn solders. Key factors affecting the reliability and solderability of the alloy includes wettability, microstructure evolution, intermetallic compound (IMC) growth at the solder-substrate interface, and mechanical properties. The addition of nanoparticles in low weight fractions reduce surface tension, enhances wettability, refines the microstructure, and improves mechanical properties such as shear strength, tensile strength, and microhardness. The improvement in mechanical properties is achieved by inhibiting IMC growth and strengthening the solder matrix. However, excessive nanoparticle additions can adversely affect the properties of solder joints. Despite advancements in lead-free solders, none of the alloys has fully replaced Sn–Pb solders due to challenges in controlling IMC formation during reflow processes. The present work reviews the effects of nanoparticles on the microstructure, mechanical properties, and reliability of SAC solder alloys. The ongoing research on nanocomposite solders should focus on optimizing nanoparticle additions to enhance reliability under thermal cycling and aging conditions. © © 2025 by ASTM International.